New pump!


Well, newer.  This shiny pump is out of a 1998 Ford Mustang.  $65 from the local scrapyard.  While it is not exactly the same as the old pump they are definitely first cousins.  Lets see how close…


Here is the biggest hurdle cleared.  The hose fittings are the same size and in the same place.  I am really sort of surprised by this but I will take my good fortune.


The electrical connector is very different.  I popped the terminals out so I could test the pump.  Here is another difference between the two pumps.  The old pump had three leads, two power and one ground.  Each power lead is a direction.  The new pump only has two leads.  I suspect the Ford circuit alternated power and ground on the two leads to change direction.  I think I know how to do that with two relays.  But later.


The pump is still full of hydraulic fluid so I put it in this container to test.  It runs great!  And I was right about the leads reversing.


Here is the next hurdle.  I have to get the mounts sorted.  This end is easy, the mounting plate is screwed to the pump body so I can swap them grommets and all.


The other end is spot-welded on so I had to carefully pry the grommet out of the old pump and put it into the new one.  For 50-year-old rubber it was not in too bad a shape.  This picture shows the grommet in it’s new home.


Next I soldered on the old pump connector on the new pump.  I almost went with replacing the old connector but this way it will look more original for whatever that is worth.  Now I need to work out how to mount it.


Previously the mounting bolts went through from the pump side.  I tried this instead.  I put the bolts through from the taillight cavity and put nuts on the inside.   This was a very clever idea but it did not work.  The bolts don’t line up with the holes on the pump.  I will have to do it the old way.  But I need help for that and nobody is around.  Later…


In order to make the new pump work I will need two relays.  That will also reduce the load on the existing switch and wiring.  The catch is where to put the relays.  Back next to the pump would be would be easy but I need a power lead.  The wire above is one of the last remnants of whatever the previous owners were trying to do back by the taillights.  If I can find the other end of this it would make a dandy power lead.  But it vanished back in to the body work and does not appear to connect to anything under the dash.  Another unsolved mystery.  I could try to snake another wire back there but that would be a lot of work.  I think I will look under the dash next.


Here is the switch for the convertible top.  This is a two-way switch.  It has power all the time and just toggles it between the two wires running back to the pump.  Once again no fuse and all the current runs though an old switch probably sourced from the lowest bidder.  Relays!


Yup!  The red wire on the right is power.  It looks to have been made by my dad due to the absence of electrical tape and the presence of a decent spade connector.  The pink and purple wires run back to the pump.


I was going to draw up a diagram of how this should be wired but then I remembered we have the internet and found this one instead.  This is a little fancier than I will need but the key elements are there.  The two motor power leads will go to the power lead (30) on the two relays.  Power from the battery will go to the normally open relay terminals (87).  The normally closed relay terminals (87B) will go to ground.  Accessory power from the key switch will go to the existing switch.  Each side of the existing switch will tie to the coil of one of the relays (86).  The other side of the coil (85) will go to ground.

So here is how this will work.  When the key off and/or the switch is not being pushed the coils will not get power and both relays will shunt the motor leads to ground.  With the key on the driver can push the switch.  That will power one relay coil which will put battery voltage on one motor lead.  Since the other relay is unpowered the other lead will be grounded and the motor will run.  Now I just have to do it.

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